Category Archives: Object ID

Identification – deer calcaneus

It looks like a calcaneus bone, which in humans and other primates is the heel bone of the foot. This one is from a left leg. In most non-human mammals it looks like it’s halfway up the hind leg, but serves the same purpose as the attachment point of the calf muscles (gastrocnemius and soleus), and its length acts as a lever to make the muscle action more powerful when flexing the foot towards the ground.

Black background with a tape measure vertical, centre-left and a bone vertical, centre-right. the bone is wider top than bottom, with points at top and top left.

Mystery bone © S Moore

As a tentative ID from reseraching from my desk in the UK is white-tailed deer (Odocoileus virginianus), based mainly on its size and coming from Mississippi. The bone is a bit worn so some of the sharper and edges and points are missing, but the overall shape of the wide end looks like it matches the photos here https://www.boneid.net/search/?product_cat=wt_deer&pa_anatomic-elements=calcaneus&order=DESC. The length is about right too, if you imagine adding back on the points and edges that have been worn away.

For much more information on the calcaneus bone, see this ID of a cattle calcaneus Identification – cattle hock bone

Identification – Fossil sponge in flint

Some flints do contain fossils, or look like whole fossils. Fossils inside the flints are often sea urchins, or cockles or other small shellfish. Sometimes, the whole flint looks like fossil, and this may be because the silica that created it was forced into a hollow space in the hardening chalk filled by a sponge. The silica fills the gaps in the sponge’s skeleton, and over millions of years, the skeleton itself can dissolve away and be replaced by other minerals. This skeleton is a fossil, and the flint fills the spaces left by the soft parts of the animal after they rotted away.

A grey, funnel-shaped fossil on a wooden surface

Typical funnel-shaped sponge, fossilised in flint. © L Hodgson.

The shape of this piece of flint looks a lot like a small sponge that lived on the sea floor, and was fossilised in flint as the thick mud solidified into chalk. It may have patterns inside it that show the structure of the sponge’s skeleton. The wiggly line around the widest part of the flint shows the top rim of the sponge and the rough texture of the line is the surface texture of the sponge preserved as a fossil.

More info on flint and chalk in Essex in this post from 2020. https://saffronwaldenmuseum.swmuseumsoc.org.uk/identification-flint-fossil-sponge/

Identification – Sea urchin fossil

Did you know we identify items for free? Whether it’s a rock from a field or a mystery something from the back of the shed, just bring it in to the Museum and we’ll take care of the rest! (If it’s too big or heavy, just send us an email with a photo).

This piece of flint with a strange marking on it was found in Wethersfield, near Braintree.

The flint nodule has preserved the impression of part of a sea urchin, or echinoid (pronounced ek-in-oid).

The shape you see is the external mould of a single plate of the echinoid’s ‘test’, or shell. When a sea urchin dies or is eaten, the test will often break apart into the individual plates.
Flint is formed from a silica-rich goo which hardens over time, and must have formed on top of this echinoid plate and taken its shape. The plates are made from calcium carbonate and this one will have dissolved away over time, leaving the impression behind.

The shape of the plate suggests it belongs to a species in the genus Cidaris. Saffron Walden Museum has a similar echinoid, Stereocidaris sceptrifera, fossilised in chalk, on display as no. 23 in the How Did They Live display in the geology gallery (below, top). In life, the club-like spines would have been attached to the plates. One of the Museum’s volunteers took this photo of a similar echinoid found at a chalk pit in Grays, Essex (below, bottom).

Fossil in chalk of the extinct sea urchin Stereocidaris sceptrifera, on display in the Museum’s geology gallery. SAFWM : 2020.42.23

The plate in the flint nodule (and the plates in the photos) is an interambulacral plate, which make up most the test of a sea urchin. They fill the space between the ambulacral zones, which are the areas where the urchin’s tube feet pass through the test. Tube feet are used for movement and to exchange oxygen and carbon dioxide with the water for respiration. Sea urchins have 5 ambulacra arranged in a star shape, showing that they are related to starfish.

The Natural History Museum has a good page showing the structure of a sea urchin test: https://www.nhm.ac.uk/our-science/data/echinoid-directory/morphology/regulars/intro.html

The British Geological Survey has an interesting page with good photos of similar fossil echinoids – look out for Temnocidaris (Stereocidaris) sceptrifera about halfway down, and Heterocidaris wickense at the bottom: https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/echinoids/

Another link to the NHM with photos of Stereocidaris fossils: https://www.nhm.ac.uk/our-science/data/echinoid-directory/taxa/taxon.jsp?id=1115

Identification – flint, fossil sponge

In Essex and south east England, almost every pebble on the beach and in gardens is flint. It’s a hard rock found in the Chalk, a soft, white, limestone layer that is up to 200m (600 ft) thick in north Essex and Cambridgeshire. In north west Essex, this chalk is between 90 million and 66 million years old and lies just below the soil, north of a line running from Stansted to Sudbury.

Diagram showing bedrock geology of Essex

Diagram showing the main bedrocks across a section of Essex. Chalk appears as the bedrock across northern Essex. Credit: reference 1.

Chalk started out as a thick mud on the floor of a tropical sea that covered most of Britain and north west Europe. This mud contained the remains of tiny sea creatures (plankton) which grew shells of calcium carbonate. When they died, these plankton and their shells fell to the sea floor to form a thick mud, which compacted into chalk over millions of years.

As it compacted, it squeezed out the seawater containing dissolved quartz, or silica (which comes from the skeletons of tiny sponges, a very simple animal).This silica was pushed out into gaps, cracks and burrows in the chalky mud to form nodules or layers of flint. These flints have a white outer layer (cortex), and are black inside. They can come in very complicated, bulging shapes, or with spikes, holes and cavities. Because of this, they can be easily confused with fossilised bones.

An irregular flint nodule with a white cortex. Credit: reference 2.

Some flints do contain fossils, often urchins, or cockles or other small shellfish. Sometimes, the whole flint looks like fossil, and this may be because the silica that created it was forced into a hollow space in the hardening chalk which contained a sponge. Sponges are very simple animals which live on the sea floor. They still exist today, and the earliest known fossil sponges are 580 million years old.

The silica fills the gaps in the sponge’s skeleton and, over millions of years, the skeleton itself can dissolve away and be replaced by other minerals. This skeleton is a fossil, and the flint fills the spaces left by the soft parts of the animal after they rotted away.
Sponges are hollow tube or cone shapes and have no muscles, stomach, brain or nerves. They are filter feeders that catch bacteria and microscopic plants & animals from seawater that flows through tiny channels (pores) in their body. Sponges are open at the top, and water currents flowing across the opening helps pull in water through the pores and remove it from the centre chamber, like wind blowing across a chimney.

Diagram showing water flow through a sponge's body

A simple diagram of a sponge’s body showing the pores in the sponge’s body, and the direction of water flow (blue arrows). Credit: reference 3.

A living sponge, showing the typical hollow tube shape. Credit: reference 4.

The first sponge below is preserved in chalk and is a typical funnel shape. Some fossils may have a textured ring around the top, showing the rough pattern of the sponge’s surface and pores, like in the second photo.

Figure showing typical funnel shaped sponge

Fossil of a sponge (Ventriculites species) that lived in the Chalk sea. This sponge attached to the sediment with its branching roots. © SWM.

Figure showing rim imprint of a sponge's body in flint.

A flint nodule showing the imprint of the upper rim of a sponge’s body. Credit: reference 5

References

Essex Bedrock, Essex Rock 1999. GeoEssex.org, retrieved 11:36, 24.4.2020
© G Lucy. GeoEssex.org, retrieved 11:31, 24.4.2020
Adapted from: Porifera_body_structures_01 By Philcha – Own work, CC BY-SA 3.0
NOAA Photo Library reef3859 By Twilight Zone Expedition Team 2007, NOAA-OE. , Public Domain,
Flint rim print. flint-paramoudra.com, retrieved 11:47, 24.4.2020

Identification – cattle hock bone

Cattle right-side calcaneus (heel bone)

The calcaneus in humans is the heel bone, and is the first point of contact with the floor when we walk. However, cattle are ‘nail-walkers’ – walking on the very tips of their toes with the rest of the foot held off the ground. This means the first joint from the ground on the hind leg is the ankle (hock), not the knee, which is why it bends in the opposite direction to our knee. The knee is further up the leg, almost hidden by the leg muscles, while the hip is very high up, just below the base of the tail.

Diagrom to show position of hock in cattle leg

The hock bone (calcaneus) is shown by no. 32 (bottom right). 31 shows the ankle joint and 30 shows the knuckles of the toes. 27 shows the knee joint (bottom middle). Image credit: reference 1.

The bovine foot has 15 bones, grouped into 7 tarsals (talus, calcaneus, and five others), 2 metatarsals (running from the tarsals to thethe two toes). These correspond to the 3^rd and 4^th metatarsals in human feet The big toe has the first metatarsal). The cow has 6 phalanges (three in each toe).
For comparison, humans have 26 foot bones, comprising 7 tarsals, 5 metatarsals (one leading to each toe) and 14 phalanges (two for the big toe and three for every other toe).

Diagrams showing skeletons of the cattle and human foot.

15-21 are the ankle bones, 23 and 24 are the metatarsals, and 26-28 show the three phalanges in each toe. The same bones are labelled in the human foot on the right. Image credits: references 2 and 3.

(The image above actually shows the front leg of a cow, with the wrist and not the ankle bones, but the other bones are generally the same.)

The original bone I was asked to ID. © Saffron Walden Museum.

In life, this cattle calcaneus is from the right hock and has the smooth side faces outward to the right, as in the photo above. The shaft of the bone is then pointing up and back, toward the tail of the animal, to form the distinctive point of the hock in the cow’s leg (no. 32 in the first diagram). The top of the bone is the attachment point for the large muscles of the lower leg. These are the gastrocnemius and soleus, (the ‘calf muscles’ in humans).

Some of the more fragile edges of this calcaneus are missing, but you can still see the main features.

This photo is pretty much a close-up of the photo above, from the bottom end. © Saffron Walden Museum.

In the photo, the letter A shows a smooth articular surface for the 3^rd and 4^th metatarsals, and B is one of the articular surfaces with the talus. C is a dome-shaped articular surface for the lateral malleolus, a bone on the outer edge of the hock. The roughened depression (D) in the centre of the plate is called the tarsal sinus, and is mirrored by a similar area on the talus. This cavity houses blood vessels, fat, nerves, and a series of ligaments which hold the tarsal bones together.
The talar shelf (E), is at the near end of the shaft, and helps support the talus bone which sits above it. There is also a groove (F) for the tendon of the flexor digitorum lateralis muscle, which bends the toes.

The calf muscles which attach to the top of the bone help straighten the leg when walking and running, while the length of the bone acts as a lever to amplify their effect and increase make the movement more efficient This is especially important in animals such as cattle, whose ancestors and wild relatives migrate across continents and run to escape predators.

– James Lumbard, Natural Sciences Officer.

References

1. Domestic_animals;_ _history_and_description_of_the_horse,_mule,_cattle,_sheep,_swine,_poultry,_and_farm_dogs,_(1858)_(14598393827)
By Internet Archive Book Images – https://www.flickr.com/photos/internetarchivebookimages/14598393827/Source book page: https://archive.org/stream/domesticanimalsh00alle/domesticanimalsh00alle#page/n51/mode/1up, No restrictions, https://commons.wikimedia.org/w/index.php?curid=44520464

2. Cattle hock skeleton diagram © https://www.dcfirst.com/cow_skeletal_anatomy_poster.html Accessed 31.3.2020.

3. BruceBlaus. :Blausen.com staff (2014). “Medical gallery of Blausen Medical 201”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. / CC BY 3.0

Identification – Limonite

Limonite (pronounced “lime-on-ite”) is an iron ore similar to the more well-known iron oxides haematite and magnetite. It often forms as existing deposits of these other minerals react with water in an oxidation reaction, turning the iron oxide into iron oxide-hydroxide. This interrupts the regular crystal structure and opens up microscopic gaps that trap other water molecules in positions where they can’t chemically react and bond with the iron atoms. Water which forms part of the molecular structure of in this way is called ‘water of crystallisation’.

Limonite can be ground up to produce the pigment yellow ochre, famous from prehistoric cave paintings. This sample from the Museums’ mineral collection has yellow limonite on brown goethite, another form of iron hydroxide.
Image: © Saffron Walden Museum.

Scientifically, limonite does not meet the criteria of a ‘true’ mineral, which must have a consistent chemical formula and molecular crystal structure. Because limonite forms as a replacement for several other minerals, this means that the crystal structure is not consistent. Variations in the original mineral, the compounds dissolved in the water and the environment where it forms, also mean the relative amounts of iron oxide, iron hydroxide and water of crystallisation are not constant either.

These pieces of limonite were originally pieces of the gemstone garnet. Iron-rich water filtering through these stones replaced the original garnet mineral with limonite, keeping the shape.
Image: Eurico Zimbres FGEL/UERJ CC BY-SA 2.0 br (Wikimedia Commons)

Limonite may be any colour from a rich yellow to a dark brown, and was used historically to make the yellow ochre pigment which is still produced in this way in Cyprus. Despite this variation in colour, an easy way to distinguish it from haematite is the ‘streak test’. This can be used to separate many minerals which may appear similar to the eye, by rubbing the mineral along a piece of un-glazed white porcelain. Limonite will leave a yellow-to-brown streak, whereas haematite produces a red streak.

Two forms of haematite leave a rusty red streak on ceramic, central.

Two different forms of haematite both leaving a rust-red streak.
Image: KarlaPanchuk [CC BY-SA 4.0] (Wikimedia Commons)

Deep red botryoidal (grape-like) haematite.

This is an easily-recognised form of iron oxide, haematite. The rounded, bulbous form is described as ‘botryoidal’, meaning grape-like in Greek.
Image: © Saffron Walden Museum

– James Lumbard, Natural Sciences Officer.

Identification – Ammonite in sandstone

One of the most interesting parts of working in museums is helping people discover something new (and I usually learn something new myself). A really important way for museums to do their job as a welcoming public source of information is by identifying mystery objects that you might find on a walk, on a seaside holiday or even in your garden or attic.
Anyone can bring in an item for us to identify, for free, and you should have an answer within a few weeks. It might look a bit like this:

Ammonite in sandstone

[Show slideshow]

This piece of stone is a Jurassic fine-grained sandstone or sandy limestone, which may be from the Lias Group rock unit found on the Dorset coast, although it has a sandier appearance and rougher texture than the rocks usually found in this formation. If it is from the Dorset Lias formation, the rock is roughly 195 to 200 million years old, and the fossils it contains would be a species of Promicroceras ammonite, which are common along the Dorset coast.

Fossil of a Promicroceras ammonite.
Image: Ammojoe CC BY-SA 3.0 (Wikimedia Commons)

The bristleworm, Polydora ciliata. Image: Yale Peabody Museum of Natural History [CC0] (Wikimedia Commons)

The surface pattern of pores in the rock was made much more recently. They were probably made by a species of Polydora worm, probably Polydora ciliata. P. ciliata is a small, rock- or shell-boring worm which can grow up to 30mm (1 1/8 in.) long, and is also known as a bristleworm.

P. ciliata burrows in stone. Image: Rosser1954 CC BY-SA 3.0 (Wikimedia Commons)

Bristleworms are thought to burrow into rock or shell by scraping away at the surface using specialised bristles on the fifth segment of its body, although it may also secrete chemicals such as weak acid to help. It digs a U-shaped burrow, which appears on rocks as distinctive small slots or a ‘sunglasses’ shape.

– James Lumbard, Natural Sciences Officer.

Ammonite in sandstone

A close-up of the stone showing the surface pores and a fossil, with ruler for scale. © Saffron Walden Museum.

The whole stone showing surface texture, a fossil and a ruler for scale. © Saffron Walden Museum.

A close-up shot of a second fossil, with ruler for scale. © Saffron Walden Museum.

Close-up shot showing what seems to be fine layering in the stone. © Saffron Walden Museum.

The whole piece of stone showing surface pores. © Saffron Walden Museum.